Such a seat cushion is known from DE-U-296 22 187.
Similar seat cushions are known from U.S. Pat. No. 5,634,223 or EP-B-0 705 549.
The disadvantage in the known, essentially round seat cushions is that for the user of the seat cushion when sitting on it they have only inadequate support especially for the thighs of the user if they do not have a correspondingly large diameter and project into the area of the thighs of the user.